You may have noticed that your MRE's have a funny number at the bottom. The time scale that is the basis for Julian dates is Universal Time. Julian Dates, abbreviated JD, are simply a continuous count of days and fractions since noon Universal Time on January 1, 4713 BCE (on the Julian calendar). Adoption of the Gregorian calendar in the rest of the world progressed slowly.
We refer to a yyddd date format (yy = year, ddd=day) as a 'Julian Date' - this is the common term for such a date in mainframe and other circles.The current Julian cycle started on January 1, 4713 B. (Gregorian calendar) and will end on January 22, 3268 A. Julian date is commonly used in computer science to calculate the difference between days, since all numbers in the system are consecutive integers.